1. Field of the Invention
The present invention concerns a magnetic recording/playback head comprising a superconducting material and, in particular, a magnetic head in which a superconducting material is used to channel the magnetic flux emitted by the head towards the magnetic recording support.
2. Description of the Prior Art
To highlight the value of the invention, we shall first give a general description of existing magnetic recording/playback heads.
Magnetic recording/playback heads consist of a magnetic circuit 1 of high permeability, comprising a non-magnetic gap 2, of a thickness e, and an electrical circuit 3 which surrounds the magnetic circuit 1 (FIG. 1).
When the circuit 3 is crossed by a current, it emits a magnetic field H which is picked up by the circuit 1 and gets concentrated at the gap 2. Conversely, a local flux variation at the gap 2 induces a voltage V at the terminals of the circuit 3.
Presently available heads can be divided into two groups:
massive heads made by machining and assembling semi-heads made of magnetic material (for example, audio heads made of or magnetic material, domestic video (VHS) type heads made of ferrite monocrystal). The circuit 3 is coiled after assembly;
thin layer heads, such as those shown in FIG. 2, made by successive deposits of thin layers of magnetic materials of dielectrics and semi-conducting tracks etched so as to make the elements 1, 2 and 3.
Each of these groups can be used:
either for longitudinal recording, i.e. with a recording medium in which the magnetization is parallel to the support and to the flow of the tape;
or with recording perpendicular to the vertical, i.e. with a recording medium in which the magnetization is perpendicular to the support and to the flow of the tape.
For this second type of recording, it may be preferable to use heads in which the magnetic circuit 1 is not closed at the gap 2 by two symmetrical poles, only ore of the poles playing an active role in the recording. This pole is then the main pole or a single pole head.
The main criterion for characterizing a head is the signal-to-noise ratio which should be as high as possible.
.eta. the value of the signal is determined by efficiency (in recording and by reciprocity in playback). .eta.=H9x)/Ho with H(x)=magnetic field during recording at a distance x from the gap. ##EQU1## i=current in the circuit 3
n=number of rotations of the circuit 3
e=thickness of gap.
the intrinsic noise of the head (thermal noise) is proportionate to the real part of the impedance ##EQU2## with
p=resistivity of wire of circuit 3
1=length of wire proportionate to number of revolutions of circuit 3
s=section of wire
L=inductance of head proportionate to n2.
.mu.".sub.e =imaginary part of the effective permeability of the magnetic circuit.
.mu.'e=real part of the effective permeability of the magnetic circuit.
The object of the invention, therefore, is to provide means which can be used to increase the signal-to-noise ratio of a magnetic head.
The invention can be applied to different types of heads, and it particularly concerns:
massive heads for longitudinal or perpendicular recording.
thin layer heads for longitudinal and, if necessary, perpendicular recording.
main pole or single pole heads for perpendicular recording.